1. Field of Invention
This invention relates to pistons for use in internal combustion engines. More particularly, it relates to a piston for use in a diesel engine having a double tapered top land which provides for controlled variation in clearance between the piston and cylinder wall above the top compression ring of the piston.
2. Description of the Prior Art
For many years it was the practice of diesel engine designers to minimize the clearance between the piston and cylinder wall in an attempt to prevent the accumulation of carbon deposits about the piston. These close clearances failed to reduce hard carbon and thus oil consumption was adversely affected. Further, the hard carbon build-up caused ring and liner wear thereby shortening the effective life of the engine.
Recently, it has been found that by manufacturing the piston with a relatively large set back for the top land and thereby providing a relatively large annular space about the piston head above the top ring, load bearing carbon deposits could be minimized without affecting the seal provided by the top ring. While this piston design achieved the desired result of reducing oil consumption and wear, other aspects of engine performance such as emissions, smoke, and fuel consumption were adversely affected.